1. Field of the Invention
This invention relates to a pressure relief vent for a pressurized container.
2. Description of the Prior Art
Pressurized containers are widely used for a number of purposes which include, but are not limited to: (a) storage of gases such as oxygen, nitrogen, natural gas and propane; (b) packaging and dispensing consumer products such as paints, lacquers, varnishes, food products, hair spray, deodorants, shaving lather, insecticides and herbicides; and (c) packaging for electrochemical cells. The pressurized containers used for packaging and dispensing consumer products are typically aerosol containers which contain a product which is mixed with a propellant gas such as freon.
Pressurized containers are potentially dangerous because of the possibility that an explosion can result upon overpressurization. Such overpressurization can, of course, result when such a container is abused upon filling. More frequently, however, overpressurization results when the container and its contents are abused by exposure to elevated temperatures during incineration or by storage at unacceptably high temperatures. Overpressurization can also occur as the result of chemical reactions taking place within the container, such as in a sealed storage battery which releases gases internally upon overcharge or overdischarge. For example, lithium batteries are desirably enclosed in a casing which contains a pressure release vent to prevent any possibility of accidental explosion, and such batteries which utilize sulfur dioxide as an electrolyte component desirably have a vent that operates at about 350 psi.
One conventional method for incorporating a pressure release vent into a container involves the insertion of one or more score lines in a wall of the container in order to provide a point of weakness at which venting will take place upon overpressurization. For example, U.S. Pat. No. 3,292,826, issued to Abplanalp on Dec. 20, 1966, discloses a pressure relief vent which is formed by at least partially circumscribing a relatively large section of the container wall with a score line. Similarly, U.S. Pat. No. 4,256,812, issued to Tamura et al. on Mar. 17, 1981, discloses a pressure relief vent which consists of two score lines in the container wall which cross each other to form a cruciform incision.
U.S. Pat. No. 3,918,610, issued to Willis on Nov. 11, 1975, discloses a safety vent for a pressurized container which comprises: (a) an integral concavity in the container wall, (b) an integral hollow bridge interrupting said concavity, and (c) a weakening score line in the container wall transversely across the hollow bridge. Excessive pressure in the container acts to stress the bridge and results in a fracture of the residual container wall under the weakening score line. The approach set forth in this patent is not, however, entirely satisfactory. In a vent of this design, the wall thickness under the score line is a critical parameter if operation is to reliably take place at a predetermined pressure, and thickness tolerances for proper venting are undesirably small.